The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A006881

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A006881

Squarefree semiprimes: Numbers that are the product of two distinct primes.
(history; published version)

#248 by Charles R Greathouse IV at Sun Feb 16 08:32:31 EST 2025

LINKS

Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/Semiprime.html">Semiprime</a>

Discussion

Sun Feb 16

08:32

OEIS Server: https://oeis.org/edit/global/3014

#247 by Charles R Greathouse IV at Mon Jan 13 09:59:29 EST 2025

STATUS

editing

approved

#246 by Charles R Greathouse IV at Mon Jan 13 09:59:22 EST 2025

FORMULA

a(n) ~ n log n/log log n. - Charles R Greathouse IV, Jan 13 2025

STATUS

approved

editing

#245 by Michael De Vlieger at Tue Oct 29 15:40:34 EDT 2024

STATUS

proposed

approved

#244 by Michel Marcus at Tue Oct 29 15:33:47 EDT 2024

STATUS

editing

proposed

#243 by Michel Marcus at Tue Oct 29 15:33:38 EDT 2024

FORMULA

For k > 1: k is a term of a <=> k^A001221(k) = k*A007947(k).

For k > 1: k is a term of a <=> k^A001222(k) = k*A007947(k).

For k > 1: k is a term of a <=> A363923(k) = k. (End)

STATUS

approved

editing

#242 by R. J. Mathar at Sun Aug 18 10:04:47 EDT 2024

STATUS

editing

approved

#241 by R. J. Mathar at Sun Aug 18 10:04:40 EDT 2024

LINKS

R. J. Mathar, <a href="https://arxiv.org/abs/0803.0900">Series of reciprocal powers of k-almost primes</a> arxivarXiv:0803.0900, table 6 k=2 shows sum 1/a(n)^s).

#240 by R. J. Mathar at Sun Aug 18 10:03:53 EDT 2024

LINKS

R. J. Mathar, <a href="https://arxiv.org/abs/0803.0900">Series of reciprocal powers of k-almost primes</a> arxiv:0803.0900, table 6 k=2 shows sum 1/a(n)^s).

STATUS

approved

editing

#239 by Michael De Vlieger at Fri Aug 16 08:37:38 EDT 2024

STATUS

reviewed

approved